Association of PM_2.5 components and green environment exposure levels with the recurrence of ischemic stroke in Tianjin, China: a time series analysis from 2019 to 2020

Objective To assess the association of PM_2.5 component exposure with ischemic stroke (IS) recurrence, and to investigate the modulating effect of green environments.

Methods Data on hospitalized patients with recurrent IS, air pollutants, and meteorological conditions in Tianjin from January 1, 2019 to December 31, 2020 were collected. A generalized linear model based on Poisson regression was employed for time series analysis to quantify the excess risk of IS recurrent hospital admissions associated with each IQR increase in PM_2.5 components. The effects of PM_2.5 components on IS recurrence were analyzed at different levels of greening, stratified by the normalized difference vegetation index (NDVI).

Results Short-term exposure to PM_2.5 components, including elemental carbon (EC) and zinc (Zn), showed a significantly positive association with the risk of IS recurrence. This association also held for iron (Fe) with a cumulative lag of 1 to 3 days. All three components showed the most significant effects at a cumulative lag of 3 days. For each IQR increase in EC, Zn, and Fe, the risk of IS recurrence-induced hospital admissions increased by 4.64% 95% confidence interval (CI): 2.63%-6.69%, 4.22% (95% CI: 2.06%-6.42%), and 3.42% (95% CI: 0.52%-6.41%), respectively. In low-greening environments, organic carbon (OC), EC, and Zn had more significant effects on IS recurrence, while the negative effects of these pollutants were effectively mitigated in high-greening environments.

Conclusion Elevated levels of EC, Zn, and Fe in the PM_2.5 components increase the risk of IS recurrence-induced hospital admissions, and greening exposure has a potentially protective effect.